A superhabitable planet is a world that might have an even better chance of supporting life than our own home, Earth.
Because Earth is the only known inhabited planet and its life depends on liquid water, efforts to identify exoplanets which could harbor life concentrated on Earth-like worlds. But some researchers believe there are other types of planets that could offer living conditions as good as – or even better than – Earth. In fact, some scientists argue that focusing only on Earth-like worlds might be too “anthropocentric and geocentric,” blinding us to the possibilities of exobiology.
“We are so focused on finding a mirror image of Earth that we risk overlooking a planet even more suited to life,” said Dirk Schulze-Makuch, an astrobiologist at Washington State University and at the Technical University of Berlin. Space.com.
How do scientists search for superhabitable planets?
To search for potentially superhabitable exoplanets, Schulze-Makuch and his team investigated the Kepler Object of Interest Exoplanet Archive, focusing on 4,500 planetary systems that likely had rocky planets in their midst. stars‘ habitable zones, where liquid water can persist. The researchers published their findings in a 2020 article in the journal Astrobiology.
In addition to examining planetary systems with yellow dwarf stars like our Sunscientists have also looked at orange dwarf stars, which are cooler, dimmer and less massive than our sun.
“Our sun is actually not the best kind of star to host a planet with a lot of life,” Schulze-Makuch told Space.com.
Orange dwarf stars are about 50% more common than yellow dwarfs in Milky Way. While our sun has an estimated lifespan of less than 10 billion years, orange dwarfs have lifespans of 20 to 70 billion years. Since complex life took about 3.5 billion years to appear on Earth, the longer lifespans of orange dwarf stars could give planets in their habitable zones more time to develop life and increase biodiversity. .
Earth is about 4.5 billion years old, so researchers have speculated that the sweet spot for life would be a planet between 5 and 8 billion years old.
A planet’s size and mass can also influence its ability to support life, the researchers wrote. A rocky planet larger than Earth would have more living space and potentially a thicker, more stable atmosphere. A planet about 1.5 times the mass of Earth would likely retain its interior heat longer, which would help keep its core molten and its protective magnetic field active for a longer period during which life could have the chance to appear and evolve.
Worlds that are slightly warmer than Earth by about 8 degrees Fahrenheit (5 degrees Celsius) could be superhabitable because they might have larger tropical areas which, on Earth, support more biodiversity. However, hotter planets might also need more humidity, as greater heat could expand deserts.
Additionally, planets with the same land area as Earth but divided into smaller continents might be more habitable. When continents become particularly large (like Earth’s ancient continent Gondwana about 500 million years ago), their centers are moved away from the oceans, often rendering the interiors of large continents vast deserts inhospitable. Additionally, Earth’s shallow waters have greater biodiversity than its deep oceans, so scientists believe that planets with shallower waters may harbor more life.
What are the superhabitable planets?
In total, Schulze-Makuch and his team identified 24 potentially superhabitable planets. None of these worlds met all the criteria established by the researchers for superhabitable planets, but one met at least two – KOI 5715.01.
KOI (Kepler Object of Interest) 5725.01 is a planet about 5.5 billion years old and 1.8 to 2.4 times the diameter of Earth orbiting an orange dwarf at about 2,965 years- light. It could have an average surface temperature about 4.3 degrees F (2.4 degrees C) colder than Earth’s, but if it has more greenhouse gases than Earth to trap heat , it could be superhabitable, the researchers wrote.
Schulze-Makuch’s favorite potentially superhabitable world of those 24 was KOI 5554.01. This planet is about 6.5 billion years old, with a diameter of 0.72 to 1.29 times that of Earth, orbiting a yellow dwarf about 700 light-years from Earth.
“I really liked the average surface temperature – around 27 degrees C [80 degrees F]”, Schulze-Makuch said. “And it’s probably about the size of Earth, and a bit older than Earth.”
These 24 potentially superhabitable planets are more than 100 light years from Earth. That makes them too far for NASA Transiting exoplanet study satellite (TESS) to capture high quality images and learn more about them.
Still, Schulze-Makuch noted that future spacecraft, such as the newly launched James Webb Space TelescopeNASA’s LUVOIR space observatory mission concept and the European Space Agency’s PLATO space telescope, could illuminate these worlds.
“We caution that if we’re looking for superhabitable planets, that doesn’t mean they necessarily contain life,” Schulze-Makuch said. “A planet can be habitable or superhabitable but uninhabited.”
Additional Resources and Reading
If you’re excited about the idea of exoplanets, search the NASA Exoplanet Archives yourself! If you want to learn more about how different and weird other planets can be, dive into astronomer Michael Summers and physicist James Trefil’s 2017 book “Exoplanets: Diamond Worlds, Super Earths, Pulsar Planets, and the New Search for Life Beyond Our Solar System.” And for anyone who dreams of living in another world, get lost in this TED Reading List to become – and thrive as – an alien.